Heat shield for turbine strut



Allg, 30, 1966 M, SHAlNESs 3,269,700

HEAT SHIELD FOR TURBINE STRUT Filed Dec. 7, 1964 United States Patent O3,269,700 HEAT SHIELD FOR TURBINE STRUT Myron Shainess, Hartford, Conn.,assignor to United Aircraft Corporation, East Hartford, Conn., acorporation of Delaware Filed Dec. 7, 1964, Ser. No. 416,387 11 Claims.(Cl. 253-39.1)

This invention relates to turbine vanes or struts and particularly toheat shields for the strut.

Where the strut or vane is intended to form a loadcarrying structure, asshown, for example, in the Nichols and Werstler application, Serial No.337,407, iiled January 13, 1964, it may be desirable to control the rateof heating of the vane when the turbine is put in operation in order tominimize stresses resulting from differential thermal expansion of theseveral parts. For example, the inner and outer duct wall forming ringsheat up more slowly than a stmt extending across the gas path since thestrut is exposed on both sides to the hot gas whereas the duct wallrings are exposed only on one side. One feature of the invention is aheat shield surrounding the vane or strut to reduce the rate oftemperature change in the vane during transient conditions.

Another feature is a heat shield surrounding a turbine vane and somounted that it is free to expand around the vane without applying aload to either vane or shield. Another feature is a readily mounted andassembled heat shield which is held in surrounding relation to the strutor vane.

Other features and advantages will be apparent from the specificationand claims, and from the accompanying drawing which illustrates anembodiment of the invention.

FIG. l is a radial section through a turbine duct in which the vane ispositioned.

FIG. 2 is a sectional view along the line 2 2 of FIG. 1.

FIG. 3 is a fragmentary sectional view along the line 3-3 of FIG. l.

FIG. 4 is a fragmentary sectional view along the line 4-4 of FIG. 1.

FIG. 5 is a fragmentary sectional view along the line 5 5 of FIG. 4.

The invention is shown in connection with -a row of radially extendingvanes or struts 2, only one of which is shown, which form a connectionbetween an inner Iannular duct wall 4 and an outer annular duct wall 6.The vanes serve to hold these walls in predetermined spaced relation todeline between them a gas path for the flow of hot gas either to aturbine located downstream of the struts or from a turbine locatedupstream of the struts. In either event the struts are subjected tolarge temperature changes particularly when the turbine is being startedor stopped and the thermal expansion resulting from these temperaturechanges causes high stresses in the struts and in the duct walls.

Each strut has a shoud element 8 at the inner end by which it is securedwithin the duct wall, the latter in the arrangement shown being made upof spaced rings 10 and .12 between which the shrouds 8 are positionedand to which the shroud elements are secured as by bolts 14. A similararrangement is provided at the outer end of the struts where the outershroud 16 is positioned between spaced rings 18 and 20, being held bybolts 22.

For the purpose of minimizing the heating of the strut and for reducingthe rate of heating or cooling of the strut thereby allowing the ductWalls to increase in temperature more nearly -at the same rate as theincrease in temperature of the strut, the latter in accordance with thepresent invention is surrounded by a heat shield 24. This shield issupported so that it is free to expand without in any way stressing thestrut or the shield.

Referring more specifically to FIG. 2, the strut 2 which ICC is hollowhas a leading end 26 on which is mounted an elongated bracket 28, thelatter being held in position as by rivets 30. The bracket has anelongated slot 32 extending longitudinally of the strut and in aposition to receive a tongue 34 projecting inwardly from the leading end36 of the shield 24. Clearance is provided so that movement of theleading end of the shield with respect to the bracket 28 may occurchordwise of the stru-t or shield.

At the trailing end of the strut the latter has a trailing end element38 to which is attached, as by rivets 40 and 42, FIGS. 2 .and 4,respectively, a guide element 44, the latter having a tongue 46positioned in a slot 48 formed in the trailing end portion 50 of theshield. The latter is, in effect, made up of a single piece of materialwhich is wrapped around the strut with the opposite edges of thematerial thickened and forming the trailing end portion of the strut andbeing held together as by a row of rivets 52. Clearance is provided inthe groove 48 for `the tongue 46 to permit chordwise movement of theheat shield on the strut at the trailing edge of the latter. The guideelement 44 is bifurcated to straddle the trailing edge element 38 of thevane and the rivets 40 extend through one of the bifurcations as shownwith the rivets 42 extending through the other bifurcation.

In order to retain the heat shield in radial position on lthe strut, thebracket 28 adjacent the outer end has a n'vet 54 extending across theslot 32 and engaging in a notch 56 formed in the tongue 34. This notch56 extends axially of the assemblage and thereby locates the leadingedge of the heat shield in predetermined radial position with respect tothe leading edge of the strut, as will be apparent, without impeding thechordwise movement of the shield with respect to the strut `at thispoint.

At the trailing e-dge of the strut near vthe outer end thereof, theprojecting rib 46 is extended outwardly as at 58 to be engaged by thetwo outermost rivets 52a. At this point the groove 48 is also extendedtoward the trailing edge of the shield as shown at 60 in FIGS. 1 and 4where the rib 46 is extended. With this arrangement the heat shield islocated both axially and radially at this point. It will be apparentthat the shield Vis securely located in surrounding relation to thestrut in such a manner that it will remain in the desired position onthe strut both radially by the arrangement shown in FIG. 4 and also bythe rivet 54 and notch 56. The strut is also located axially by thearrangement shown in FIG. 4 but the axial expansion is not interferedwith by reason of .the notch 56.

Accordingly, when the turbine engine in which this invention isincorporated is set in operation and hot gases flow over the shieldsurrounding the strut, the shield will substantially reduce the rate atwhich the strut is heated so that the thermal expansion of the strutwill be more nearly at `the same rate as the thermal expansion of theinner and outer duct walls thereby minimizing thermal stresses withinthe device. Under extreme conditions it will be understood that thestrut itself may be cooled by the Icirculation of la cooling iluidthrough the strut thereby further reducing the rate of thermalexpansion.

It is to be understood that the invention is not limited v to the specicembodiment nerein illustrated and described, but may be used in otherways without departure from its spiri-t as defined by the followingclaims.

I claim:

1. A turbine strut having an operative portion of airfoil cross sectionand end shroud elements for the support of the vane, and a heat shieldsurrounding at least a part of the operative portion of the airfoil inspaced relation thereto, said shield being airfoil shape in crosssection and having means at leading and trailing edges engaging with thevane to hold the shield in spaced relation to the vane, said meanscomprising in part a grooved element extending lengthwise of the leadingedge of the vane and a projecting element internally of the shield andlengthwise thereof at the leading edge to engage the grooved element.

2. A turbine strut as in claim 1 in which a rivet extends .through the`grooved element and engages the projecting element to hold `the shieldin lengthwise position on the vane.

3. A turbine vane for use in a high temperature environrnent, including`an operative central portion over which the turbine iluid is directed,said portion being substantially airfoil shape in cross section and endshroud elements at opposite ends of the operative portion, said shroudelements holding the vane in position, and a shield around the centralportion and in spaced substantially concentric relation thereto, andcooperating guide means on the central portion and within the shield tohold the vane and shield in predetermined relation, said guide meansproviding for relative movement substantially chordwise of the shield toprovide for thermal expansion, said guide means at the leading edgeincluding a connector secured to the leading edge of the vane and havinga slot therein, and a projection longitudinally of and interiorly of theshield at the leading edge to t in said slot.

4. A turbine vane as in claim 3 in which the connector has a rivetthereon extending through the slot adjacent one end and engaging saidprojection to hold the shield in position longitudinally of the vane.

5. A turbine vane for use in a high temperature environment, includingan operative central portion over which the turbine fluid is directed,said portion being substantially airfoil shape in cross section and endshroud elements at opposite ends of the operative portion, said shroudelements holding the vane in position, and a shield around the centralportion and in spaced substantially concentric relation thereto, andcooperating guide means on the central portion and within the shield tohold the vane and shield in predetermined relation, said guide meansproviding for relative movement substantially chordwise of the shield toprovide for thermal expansion, said guide means at the trailing edgeincluding a connector mounted on the Vane and having a longitudinallyextending rib thereon extending from the connector substantially in achordwise direction, and a slot longitudinally of and interiorly of theshield at the trailing edge to receive the projecting rib.

6. A turbine Vane 4as in claim 5 in which the shield and rib have atleast one through rivet adjacent one end of the vane to hold said shieldand vane in predetermined longitudinal relation.

7. A shielded turbine vane construction for high temperatureenvironments including a vane having a central portion located in thepath of fluid through the turbine, end shroud elements for theattachment of the vane to the supporting structure, and a shield aroundand in spaced relation to the central portion, said shield beingsubstantially airfoil in cross section, and being a onepiece elementcomprising of leading edge, side surfaces extending therefrom andtrailing edge elements at the ends of the side surfaces, said trailingedge elements having cooperating surfaces and together forming thetrailing edge for the shield, and rivets holding the trailing edgeelements together when the shield is in position around the vane, saidtrailing edge elements being separable for positioning the shield aroundthe vane, said vane having a leading edge guide means and the shieldhaving a cooperating guide means adapted for assembly by relativemovement in a chordwise direction.

8. A shielded turbine vane construction for high temperatureenvironments including a vane having a central portion located in thepath of fluid through the turbine, end shroud elements for theattachment of the vane to the supporting structure, and a shield aroundand in spaced relation to the central portion, said shield beingsubstantially airfoil in cross section, and being a onepiece elementcomprising of leading edge, side surfaces extending therefrom andtrailing edge elements at the ends of the side surfaces, said trailingedge elements having cooperating surfaces and together forming thetrailing edge for the shield, and rivets holding the trailing edgeelements -together when the shield is in position around the vane, saidtrailing edge elements being separable for positioning the shield aroundthe vane, said trailing edge elements being notched lengthwise to formwhen assembled a slot, and a longitudinally extending guide element onthe vane for positioning in the slot.

9. A shielded turbine vane as in claim 8 in which the guide element onthe vane is extended adjacent one end of the vane to project between thetrailing edge elements and to be engaged and held in position by atleast one of the rivets holding the trailing edge elements together.

10. A shielded turbine vane as in claim 9 in which the shell also has aleading edge guide element and the vane has a cooperating guide elementextending lengthwise of the shell and having relative movement in achordwise direction.

11. A shielded turbine vane as in claim 10 in which a pin is located inthe cooperating guide elements to restrict the lengthwise movement ofthe shell on the vane at this point.

References Cited by the Examiner UNITED STATES PATENTS 2,500,745 3/ 1950Bloomberg 253-77 2,771,622 11/1956 Thorp 253-77 MARTIN P. SCHWADRON,Primary Examiner.

SAMUEL LEVINE, Examiner.

E. A. POWELL, JR., Assistant Examiner.

1. A TURBINE STRUT HAVING AN OPERATIVE PORTION OF AIRFOIL CROSS SECTIONAND END SHROUD ELEMENTS FOR THE SUPPORT OF THE VANE, AND A HEAT SHIELDSURROUNDING AT LEAST A PART OF THE OPERATIVE PORTION OF THE AIRFOIL INSPACED RELATION THERETO, SAID SHIELD BEING AIRFOIL SHAPE IN CROSSSECTION AND HAVING MEANS AT LEADING AND TRAILING EDGES ENGAGING WITH THEVANE TO HOLD THE SHIELD IN SPACED RELATION TO THE VANE, SAID MEANSCOMPRISING IN PART A GROOVED ELEMENT EXTENDING LENGTHWISE OF THE LEADINGEDGE OF THE VANE AND A PROJECTING ELEMENT INTERNALLY OF THE SHIELD ANDLENGTHWISE THEREOF AT THE LEADING EDGE TO ENGAGE THE GROOVED ELEMENT.